Product and process for rubber compounding



i atenteci Jan. 1, 1935 PRODUCT nssasss nn Paooriss FOR RUBBER COMlQUNDING Arthur Burnham. Cowdery, Needham; Mass., and Theodore A. Bulifant, Maywood, N. .J., assignors to The Barrett Company, New York, N. Y., a

corporation of .New Jerse No Drawing. Original application March 14, 1929, Serial No. 347,166. Dividedand this application Decembere29,*1930,' Serial No. 505,461

This application is a division of our co-pend; ing application Serial No. 347,166ffi1ed March 1.4, 1929., v

This invention relates to rubber compounding" 5 andmore particularly toapr'ocess for compound.

ing rubber involving theuse'of a softening or dispersing. agent. The invention also relates to the rubber compound resulting from the practice of this invention and also to the softeningandyor dispersing agent .employedin accordance-with our invention. r 1

Heretofcre palm oil, pinetan'mineral rubber, various pitches: and tars, and other "like materials have been added to the rubber mix fo'r the 15. purpose of dispersing the fillers such as carbon black, zinc oxide, clays, etc, used in rubber compounding: i r Coal tar distillate oil has also been used in;

rubber compounding. Th'e:oi1of this type heretoiore usedin' the industry consisted,=for ex ample, of, a fraction of about:1'.165.specific grav-' ity at 3891-6 and boiling around 300 C.," ami after cooling contained; a substantial amount ot crystalline. material which: probably consistedprincipally oft naphthalene; anthracenepphenan-fi threne and. other hydrocarbons of high molecularweight. Use of this-oil hasproven relatively satisfactory. in so faras its softeningsand dispersing qualities "are concerned; but. has been;

- found to frequently result .in serious discoloration of the finished rubberproduct and other; diflicul-b ties in -handling and processing.

.; n One object of this invention is tozprovide an agent free from the, .above "objectionspto the compounds heretofore used for dispersing; the...

fillers used in rubber; compounding which will improve 7 the dispersion of the filler in 'the xre sultant product andavoid the difficulties heretofore encountered in processing the rubberLand; 40 discoloration .of the rubber product Improved dispersion of fillers in a rubbercompound results in enhanc ement of the physical properties there-' of,particularly the "resistance of the compound or article toabrasionorwear. -.Another object i of this invention is to provide a processfor compounding rubber which-ryields a rubber product having a greater tensile. strength, greater resistance/to tear and to abrasion, and-greater resistance to crajckingjunder repeated flexing, and also having improved agingqualities. nQther objects and; advantages will: appearmfrom thefollowing detailed description, v; 2

We have discovered that'the above difiiculties attendant .upon theuse-lofiacoal tar oil as heretofore practicedyareiovercomeibyemploying coal tar oil of proper specific gravity and boiling point from. which has been eliminated the crystalline materialwhichforms therein upon standing and cooling to; normalqtemperatures. In accordance with our invention a coal tar oil fraction is selectedflwhich; after removal of crystalline material therefrom, will have a specific gravity above substantially 1.06 at 38 C. and will boil above substantially 2001 C., and the-oil is permitted to cool to about 25 C. and stand until the crystalline material which forms therein has settled.

The resultant clear oilis thenremoved ,for ex ample by decantation; The limpid oilv soproduced when compounded with rubber in accordance with the usual procedure of. forming adesired rubber compound functions both as a softening and dispersing agent. One such oil which we have employed isthemedium distillate obtained from the distillation of coal tar and having a specific gravity of 1.066 at 3810., and which when distilled to tfieftemperati'ires below indicated inthe column, at thejleft gives off the percentages by weight or; distillate indi'- cated by the figures "opposite the temperature figures;

Per-cent 210 c"! or 235 C 6.9 300 c 51.6

Another example of "a "coal tar oil which we have foundto be particularly suitable as a softeningf or dispersing agent in the compounding of rubber is the heavydistillate obtained from coal tar having a specific gravity of 1.147 at538"C.,

and which when distilled to thetemperatures be.-. low indicated in the column at the left gives off the percentages by weight of distillate indicated by the figures transversely opposite the corresponding,temperaturefigures:

. Per cent more -l 2 35 c l s0ojo. 5.1 315;o 7,4 355 (3.. "20.2

As indicated, an ex c ess of of the oil defined in the above example boils'at temperatures above about 300 -C.

As previously noted, these oils areobtained as distillate fractions from the usual distillation of coal' tar such as coke over tar and the like and mayconsist of a single'fraction or a mixture of two-or more fractions. Theoils are permitted to settle and the resultant clear-oilfree or substan tially free from crystals or suspended materials at 25 C., i. e. limpid oils, are utilized for the compounding of rubber.

These oils, we have found, possess peculiarly valuable properties as softening and dispersing agents for the various pigments and fillers, such as carbon black, zinc oxide, clays, etc., used in rubber compounding. The rubber compound or article containing our improved dispersing agent may be formed by any of the usual or wellknown methods of rubber compounding.

To illustrate the advantages, of this invention the details and resultsof several tests, .made in accordance with standard and well-known methods of the rubber industry on rubber compounds each involving the same amount of dispersing agent, two of which involve the use of our invention and the other of which involves pine tar which has heretofore been generally accepted as,

a good dispersing agent, are given below:

Rubber com- Rubber compound involvpound involv- Rubber coming 5.40 parts ing 5.40 parts pound involvof coal tar oil of coal tar oil ing 5.40 parts having a having a of pine tar specific gravspecific gravity of 1.066 at ity of 1.147 at 38 C. 38 C.

Parts by Parts by Parts by Softener or dispersing weight weight weight agent 5. 40 5. 40 5. 40 Smoked sheet (rubber) 60.00 60.00 60.00 Carbon black 24. 24. 00 24. 00 Zinc oxide 5. 00 5. 00' 5.00 Steai'ic acid 2. 40 2. 40 2. 40 AntioxidanL 1. 00 i 1. 00 1. 00 Sulfur l ,1. 75 1.75 1. 75 Accelerator 0. 45 0. 45 0. 45

Total 100.00 100.00 100. 00

RESULTS OF TESTS Abrasion value (Grasselli abrader) 204 165 182 Tensile strength 4465 4755 5045 After 30 days at 70 C. in standard Geer oven te 3045 3670 3905 -Theunts f a'o lo h o bl 1 0 abr S1 n SS m t e ab Ve ta boils at temperatures not less than about 300". C.

are obtained by the following formula? in which g=grams lost by rubber sample during tests. g.=specific gravity of sample m=duration of test in minutes HP=horse power consumed The aging qualities of the resultant'rubber compound areimproved appreciably, as indicated by the results obtained by aging the samples for- 30 days at 70 C. in the standard Geer oven test.

It will be noted that byusing coal tar oils free or substantially free from crystals and suspended matter having a specific gravity above 1.06 at 38 0., preferably oils having a specific gravity from 1.06 to 1.15 at 38 C. and boiling above 200 C., as, a dispersing agent in rubber cominvention, accordingly, renders it possible to produce rubber compositions which result in rubber articles possessing greater wearing qualities than articles heretofore obtained and is applicable to the manufacture of tire treads and tubes, rubber .heels and soles, and various mechanical rubber goods where the improved qualities imparted are desirable.

' In addition to the above advantages the oils of our invention have very much less tinting poweror discoloring effect than coal tar oils heretofore used as shown by the appearance of the finished rubber products either immediately after cure, after long standing or after 30 days in the Geer aging oven.

The dispersing agent of our invention may, if subjected to extremely cold weather conditions in storage or in transportation deposit small amounts of crystalline sediment which, however, may be readily re-dissolved byheating the oil before use, to restore it to its normally. limpid condition. I

, It will be understoodthat while preferred embodiments of this invention have been described, various changes in the details thereof might be made by those skilled in the art and, accordingly, this invention is not to be limited except as defined in the appended claims.

We claim: Q

1. A composition comprising rubber compounded with a coal tar oil substantially free from crystallinematerial at 25 C.', and having a specific gravity of not substantially less than about 1.147 at'38? C. v

' 2. A composition comprising rubber compounded with a. coal tar oil and substantially free from crystalline material at 25 0., having a specific gravity not substantially less than 1.147: at 38 C., and themajor portion of which '3. A composition comprising rubber compounded with a coal tar oil substantially free from crystalline material at 25 C., having a specific gravity of about 1.147 at 38 C., and about 95% of which boils at temperatures in excess'of about300 C.

4. The step in the process of compounding rubber which comprises incorporating in the rubber mix a coal tar oil substantially free from crystalline material at 25 C., and having a specific gravity of not substantially less than 1.147 at 38? C.

. 5. The step in the process of compoundingrubber which comprises incorporating in the rubber mix a coal tar oil substantially free from crystalline material at 25 C., having a specific gravity of not substantially less than 1.147 at 38? C. and the major portion of which boils at temperatures not less than 300 C.

6. The step in the process of compounding rubber which comprises incorporating. in the rubber mix a coal tar oil substantially free from crystalline'imaterial at 25 0., having a specific gravity of about 1.147 at 38 C., and about 95% of which boils at temperatures in excess of about 300 C.

ARTHUR BURNHAM COWDERY. THEODORE A. BULIFANT. 

